An inquiry into a botched green energy scheme which sparked a political row that contributed to the collapse of powersharing government in Northern Ireland has begun hearing final submissions.

The probe is examining how costs in the Renewable Heat Incentive (RHI) scheme spiralled.

It was designed to encourage businesses to shift from fossil fuels to renewable sources like wood but ended up paying out more than it cost to fuel the burners – earning it the moniker “Cash for Ash”.

The result was an anticipated massive overspend, falling to the Northern Irish taxpayer to pick up.

The fiasco led to a political row, the resignation of Northern Ireland’s then deputy first minister Martin McGuinness and the collapse of the powersharing government in January 2017.

Stormont has since remained in suspension, leaving the region without devolved government and senior civil servants left to lead their departments.

The RHI Inquiry led by retired judge Sir Patrick Coghlin has exposed many of the failings at the heart of the scheme.

On Wednesday the inquiry returned to Stormont where Junior Counsel to the inquiry Joseph Aiken said closing oral submissions will be heard over three days.

These include from the three core participants – the Department for the Economy, Department of Finance and Office of Gas and Electricity Markets (Ofgem).

Oral submissions will also be heard from some of the 27 individuals and organisations who were granted enhanced participatory rights.

Among those are Democratic Unionist leader Arlene Foster, former Democratic Unionist minister Jonathan Bell, a number of the party’s special advisers and some senior civil servants.

The closing submissions are being heard in Committee Room 29, a move from the Senate Chamber where the public sittings of the inquiry were previously held.

One of the first matters being examined is how an application for the scheme by then DUP special adviser Stephen Brimstone was handled.

Mr Aiken said the inquiry has more than 1,000 pages of evidence in the matter.

Mr Brimstone applied to the scheme as he installed a new biomass boiler to heat a large shed and his home, to receive subsidies offered for using this type of heat source.

Internal notes within Ofgem referred to Mr Brimstone’s application as a “special case”, the inquiry heard on Wednesday.

Mr Aiken told the inquiry that when asked what was meant by the description, Ofgem said it reflected the “political sensitivity” of Mr Brimstone’s political position as well as the media speculation surrounding the scheme.

Ofgem also emphasised to the inquiry that these were “factors which merited extra diligence and greater consideration from senior management”.

“However she stressed in her witness statement addressing this issue that it nonetheless still involved the application of the normal diligence and processes as regards compliance and counter fraud investigations,” Mr Aiken added.

Anonymous complainants made allegations of fraud around Mr Brimstone’s installation.

However it was audited a number of times and found that Mr Brimstone had complied with the scheme’s rules.